Asbestos-thickened cycloaliphatic epoxy materials for use in atmospheres of arced sulfur hexafluoride and articles thereof

ABSTRACT

RELIABILITY OF POWER CIRCUIT BREAKERS AND OTHER EQUIPMENT CONTAINING PARTS SUBJECTED TO AN ENVIRONMENT OF ARCED SULFUR HEXAFLUORIDE IS IMPROVED BY USING A CYCLOALIPHATIC EPOXY RESIN FILLED WITH ALUMINUM TRIHYDRATE AND THICKENED WITH ASBESTOS, PREFERABLY HIGHLY REFINED SHORTFIBER COALING A ASBESTOS.

United States Patent US. Cl. 260-37 EP 22 Claims ABSTRACT OF THE DISCLOSURE Reliability of power circuit breakers and other equipment containing parts subjected to an environment of arced sulfur hexafluoride is improved by using a cycloaliphatic epoxy resin filled with aluminum trihydrate and thickened with asbestos, preferably highly refined shortfiber Coalinga asbestos.

This is a continuation of application Ser. No. 775,499 filed Nov. 13, 1968 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to synthetic-resin materials in the nature of a cycloaliphatic epoxy resin provided with an aluminum trihydrate filler and asbestos thickener and having both excellent chemical resistance to an environment of arced sulfur hexafluoride and excellent arc and track resistance, i.e., resistance to degradation as a result of the passage of an electric current are along or upon surfaces of objects made of such material, and especially degradation of the kind whereby there is formed on the surface of the object a relatively low-resistance track of carbon. The invention further relates to the use of such materials in the making of parts that, when used, are subjected to an environment of arced sulfur hexafluoride, such as parts on extra-high-voltage power circuit breakers. The invention also relates to articles of manufacture made of such material.

2. Description of the Prior Art To persons skilled in the art of the transmission of electrical power at high voltages, it is known to provide the transmission lines with power circuit breakers. These are structures of substantial size, being on the order of -20 feet tall and having, in the vicinity of their tops, contacts that may be opened whenever an overload occurs on the transmission line being protected by such breaker. With three-phase alternating current at a voltage on the order of 100-500 kilovolts, it is customary to use a set of three breakers, one for each phase. When the contacts of such a power circuit breaker are opened, an arc results, and it is naturally desirable that the are be extinguished as quickly as possible in order to avoid damage to the circuit breaker. Moreover, with voltages as high as indicated above, the arc may be several inches long, or even as long as a few feet.

It is also known that one desirable attribute of a power circuit breaker is extremely high reliability. If a power circuit breaker fails to operate, there may be serious consequences at the site of the cause of the overload, at the site where the power is being generated, at the site of the circuit breaker, or elsewhere in the system. In the design and construction of power circuit breakers known to those skilled in the art, it has not been customary to spare expense, since the cost of the circuit breaker is small in comparison with that of the power generating and transmitting equipment that it protects.

3,828,000 Patented Aug. 6, 1974 In about the last ten years, it has become customary in certain designs to provide the contact area of a power circuit breaker with a flow of sulfur hexafiuoride. Sulfur hexafluoride is a gas at room temperature and atmospheric pressure, and it is chemically rather inactive. It has a dielectric value substantially higher than that of air, so that an electric arc therein not only tends to be smaller, i.e., more filamentary, but also to decay and be extinguished substantially more rapidly. See, for example, the article of P. Swarbrick in the British Journal of Applied Physics, 1967, Vol. 18, pp. 419 to 426, wherein it is reported that the time constant of an arc in sulfur hexafluoride is on the order of 1 microsecond, as compared with a time constant of microseconds for a similar arc in air. As is further explained by Swarbrick, however, an electric arc causes degradation of sulfur hexafluoride into chemical entities that are extremely reactive, such as positively or negatively charged fluorine atoms and the like. These chemical entities are capable of abstracting hydrogen from molecules having an OH bond or other active hydrogens, to form hydrogen fluoride, which is extremely reactive to many insulating materials. The reactivity of arced sulfur hexafluoride is aggravated by the presence of moisture, and moisture cannot always be completely excluded from the vicinity of the contacts of a power circuit breaker.

In building power circuit breakers of the kind protected with sulfur hexafluoride, it has been customary to lead the SP gas from a compressor and high-pressure reservoir through a feed tube, wherein the SP gas is under pressure of about 250 pounds per square inch, to the vicinity of the contacts, where SP gas is maintained at a lower pressure such as 50 pounds per square inch. The feed tube may be visualized as a simple cylindrical tube, about 12 feet long, 3 inches in outside diameter, and inch in wall thickness. Prior to the present invention, it has been customary to make such feed tubes by coating a sheet of paper on one or both sides with phenolic resin and rolling the paper to form the feed tube. The paper provides the strength required for containing the high-pressure SP gas. To obtain the required strength without internal reinforcement of the resin would require the use of impractically large wall thicknesses.

Epoxy resins of various kinds are known, including ones based upon a backbone structure comprising a pair of cycloaliphatic rings joined by a bridge comprising, for example, an ether, ester or other linkage. Although it is known that epoxy resins do, in general, have desirable properties as respects strength, dielectric constant, and resistance to chemical media ordinarily encountered, the reactivity of arced SP gas is so high that many other substances, considered just as unreactive in the ordinary run of chemical media encountered, have failed in an atmosphere of arced SP gas. For example, arced SP gas attacks silica, porcelain and glass. As experience with phenolic paper feed tubes in power circuit breakers demonstrates, arced SP also attacks phenolic resin, at least to some extent. Thus, prior to our invention, there was no assurance that there could be developed a material based upon an epoxy resin that would yield results more satisfactory than those obtained with phenolic paper feed tubes.

The development of a satisfactory feed tube for use in power circuit breakers of the kind using SF involves more than finding a material that is chemically resistant to the reactive entities present in arced SP A resinous material for this purpose must also be reasonably convenient to handle and cure, and it must also possess adequate arc and track resistance.

It is known, for example, from US. Pat. No. 3,324,073 to provide a composition of matter that comprises an epoxy resin thickened with asbestos. Nothing contained in that patent, however, suggests the particular compositions of the present invention, nor their particular properties as respects resistance to chemical attack and resistance to the formation of track-type degradation in the presence of an environment of arced SP gas. The patent is of interest for its showing of a particular kind of asbestos that we prefer to use in the practice of our invention, namely, short-fiber white chrysotile asbestos.

It is also known that the feed tubes of power circuit breakers may, in use, be subjected to considerable variations in temperature, such as from minus 30 C. to 140 C. Such temperature changes cause expansion and contraction, and since the resin must be strengthened, as mentioned above, by incorporating or embedding therein a strengthening member of different material, whose coefiicient of expansion cannot be matched with that of the resin, there is a further requirement that the composition used exhibit satisfactory flexibility. Prior to this invention, it was not known how this requirement, along with the others indicated above, could be met in a composition of matter so as to afiord, for feed tubes of power circuit breakers and other parts that are subjected, when in use, to an atmosphere of arced SP gas, properties and performance characteristics superior to those parts and materials already known.

A further requirement of a suitable composition of matter for the above-indicated purpose is that it be sufiiciently thixotropic. No known resin, unmodified, would suitably resist run-otf and sagging and give the desired high and uniform build that is required in com I positions for feed tubes and related purposes. Most of the known thixotropic agents, however, such as the very finely divided silica sold under the name of Cab-O-Sil, are subject to attack by arced SP and would be expected, therefore, to be unsuitable.

BRIEF SUMMARY OF THE INVENTION We have found that, in accordance with the invention, the above-indicated problems are overcome by providing a composition of matter that comprises, as essential components, the following: (a) an epoxy resin of the kind having a backbone structure characterized by at least one, and preferably two substantially cycloaliphatic rings, and in the case of structures comprising a pair of rings and having a bridge therebetween, preferably a resin of the kind having not more than about 5 atoms in the direct chain from one ring to the other; (b) a flexibilizing agent comprising polyazelaic polyanhydride, alone or with hexahydrophthalic anhydride; (c)a filler promoting arc and track resistance, such as aluminum trihydrate or naturally occurring magnesite; and (d) short-fiber or finely divided asbestos, preferably short fiber white chrysotileasbestos, highly refined, as a thixotroping agent. When the above components are mixed, for example, in such proportions as 100 parts by weight of resin, 75 parts by weight of polyazelaic polyanhydride, 175 parts by weight of aluminum trihydrate and 1.75 to 3.5 parts by weight of asbestos, alone or with a suitable catalyst or accelerator, there is obtained a viscous liquid that can advantageously be used, as herein taught, to serve the purposes and overcome the problems indicated above. More particularly, this viscous liquid itself or thinned with suitable organic solvents, is applied to objects and cured. A particular example involves making a power circuit breaker feed tube by applying the viscous liquid of this invention to a mandrel, causing it to cure, wrapping resin-wet glass fiber therearound, curing, grinding the outside diameter to size, applying additional amounts of the viscous liquid to the sized exterior, and again curing. Alternatively, a feed tube is made by wrapping glass fiber wet or impregnated with the viscous liquid on a mandrel, curing, grinding to size, removing the mandrel, and applying the viscous liquid to the interior and exterior of the glass fiber tube so formed, as by spraying, brushing, dipping or casting.

4 DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the invention, there is compounded a composition of matter comprising an appropriate resin, a flexibilizing agent, a filler, and asbestos as thickener or thixotroping agent. The mixture may also contain if desired, a catalyst or a reaction accelerator that participates in the curing reaction. Those skilled in the art will appreciate that the above-mentioned components may be used in different amounts and proportions, depending upon the properties desired and the particular components selected.

The epoxy resin selected is substantially cycloaliphatic and is preferably of the kind having a backbone structure comprising a pair of cycloaliphatic rings joined by a bridge, with epoxy oxygen atoms disposed between vertical ones of the carbon atoms comprising the cycloaliphatic rings. The cycloaliphatic resins are used in place of the other known kinds of epoxy resins, such as the ones of aromatic character, based upon a bisphenol, or the epoxidized novolac resins. The resins of cycloaliphatic character appear to yield compositions having the desired flexibility, chemical inertness, and resistance to surface arcing, whereas test with epoxy resins of the other kinds mentioned above, or with other synthetic resins, tended generally to yield results that were deficient with respect to one or more of the above-mentioned properties. For example, bisphenol-type epoxy resins were tried, but these lacked, because of their aromatic nature, the desired high order of arc and track resistance in moist highpressure SP The novolac epoxy resins were sufficiently chemically resistant, 'but they were also deficient in arc and track resistance in moist SP Polyesters, such as polyethylene terephthalate, were not sufiiciently chemically resistant to arced SP The same was true of the poly urethanes and the polyamides that were investigated. The silicone rubbers and resins were investigated, but these were very poor in chemical resistance to arced SP The polyphenylene oxide resins had adequate chemical resistance, but failed in the are and track test. The polyolefins, such as polyethylene and polypropylene, proved satisfactory in both chemical resistance and are and track resistance, but only when care was taken to produce a composition free of harmful catalyst and stabilizer. Moreover, these materials are difiicult to use for the purposes of the invention, since it is not easy to form and cure a coating based upon them that also contains the other desired ingredients. They are also undesirable as they are thermoplastic, i.e., are heat-meltable.

Applicants are aware of two kinds of cycloaliphatic epoxy resins that are now commercially available, and of these, one having a backbone structure that comprises two cycloaliphatic rings joined by a bridge structure of in comparison with those obtained with the other, which has a bridge structure of That is to say, the resin with the shorter bridge structure appears to be preferable, being less flexible and therefore less subject to permeation by active chemical entities existing in arced SP Thus, it may be said that in the practice of the invention, it is preferred that there be used a cycloaliphatic epoxy resin that has a bridge between its rings that does not contain more than about 5 atoms in the direct chain between said rings.

To be more precise, a preferred kind of cycloaliphatic epoxy resin suitable for use in practicing the present invention is that having the backbone structure where R is a cycloaliphatic ring, preferably but not necessarily a fi-membered aliphatic ring, having an epoxy oxygen atom connected to a pair of vicinal carbon atoms thereof, with a viscosity at 25 C. of 350-450 cp. and an epoxide equivalent weight of 126-140. Such resin is sold by Union Carbide Chemical Co. under the mark ERLA 4221, and by Ciba Chemical Co. under the mark CY- Another resin satisfactory for the practice of the invention is that having a backbone structure of which may be designated 2,3-epoxy cyclopentanelf l-endomethylene cyclohexane-G-glycidyl ether. Such resin is sold by Ciba Chemical Co. under the mark CY-181.

There is also the diglycidyl ester of tetrahydrophthalate anhydride, the compound COCH;CHCH:

|l O O which is sold by Ciba Chemical Co. under the mark CY-182 and by Union Carbide Chemical Co. under the mark ERX-49 and constitutes a different epoxy-resin monomer useful in the practice of the invention.

There is, moreover, the resin based upon the diglycidyl ether having the formula i.e., the diglycidyl ether of hexahydrophthalic anhydride. Such ether is sold by Ciba Chemical Co. under the mark CY-183 and by Union Carbide Chemical Co, under the mark ERIKA-4090.

Other resin monomers useful in the present invention are those based upon the reaction product of epichlorohydrin with hydrogenated bisphenol-A, i.e., a compound of the formula O CH: 0

Such monomer is sold by Ciba Chemical Co. under the mark CY-185.

Yet other epoxy-resin monomers useful in the practice of the present invention are those based upon the diglycidyl ether.

where n =an integer from about 4 to 30; and R and R are lower alkyl radicals such as C to C Such monomers are sold by Ciba Chemical Co. under the mark Araldite 508 and by Dow Chemical Co. under the mark DER-732. Though chemically similar and generally capable of being substituted for each other, the two above-mentioned commercial products differ somewhat, their room-temperature viscosities being 2500-5000 cp. and 55-100 cp., respectively.

Still other epoxy-resin monomers useful in the practice of the present invention comprises the di-(epoxy cyclopentane) ethers of the kind that are sold by Union Carbide Chemical Co. under the mark ERRA-4205. These comprise an isomeric mixture of such epoxycyclopentane ethers, one of which has the formula One hundred parts by weight of such resin are mixed with further ingredients as mentioned below.

The composition further contains 30-115 parts by weight per parts of resin, of a flexibilizing agent comprising polyazelaic polyanhydride having an appropriate molecular weight of 2100-2500 and/ or hexahydrophthalic anhydride. There may be used, for example, 75 parts by weight of the polyazelaic polyanhydride; or 60 parts by weight of the polyazelaic polyanhydride and 10 or 15 parts of the hexahydrophthalic anhydride. As a flexibilizing agent, the latter is less effective than the former. When the composition lacks an adequate proportion of effective flexibility agent, cracking develops when the cured composition coated on, for example, filament-wound-glass epoxy structures, is subjected to a thermal cycling test. 0n the other hand, compositions that contain too great an amount of flexibilizing agent, while satisfactory in the thermal cycling test, tend to exhibit poor or unsatisfactory results in a chemical attack test comprising exposure to arced SF gas. In some instances, especially when the base resin is itself particularly flexible hexahydrophthalic acid may be used alone, but in most instances, about 70- parts of the polyazelaic anhydride per 100 parts of resin are needed to obtain adequate flexibility to pass the thermal cycling test hereinafter described.

The composition further comprises aluminum trihydrate or naturally occurring magnesite, preferably the former, as a filler promoting arc and track resistance in moist SP gas. There may be used, per 100 parts of resin, about -250 parts by weight of such material. No sub stitute for such material, for the purposes of this inven- .tion, is known. Without it, the arc and track resistance in moist SP gas is poor. The trihydrate has the further attribute that it is sufiiciently basic in character that, in addition to serving the purpose mentioned above, it also is capable when the mixture is subjected to curing conditions hereinafter mentioned, of promoting the usual intermolecular cross-linking between the epoxy oxygen atoms of the resin that characterizes such curing. Those skilled in the art of working with epoxy-resin compositions will appreciate that such curing is customarily promoted with the use of an agent of fairly strongly acidic or basic character. When the magnesite is used, it becomes necessary to use, for one example, benzyldimethylamine as the catalyst to promote the curing reaction.

The composition further comprises asbestos of short fiber or fine grain size as a thixotroping agent. In the invention, the use of a satisfactory thixotroping agent is absolutely essential. Without one, the filler tends to settle out when the composition is used for casting or potting, and when the composition is used for spray or dip casting, the thixotroping agent is needed in order to prevent most of the coating from dripping off the coated piece as soon as it is subjected to curing heat. One of the commonly used thixotroping agents in epoxy-resin compositions is very finely divided silica, but this material is completely unsatisfactory for use in the present invention because of the great susceptibility of silicon-containing compounds to attack by reactive components present in arced SF gas. Mediumor long-fiber asbestos is not satisfactory, but satisfactory results are obtained with finely divided asbestos (about 0.5-10 micron particle size), such as that sold by Food Machinery Corporation under the name Avibest, so long as the composition is used for casting or in some other way providing a smooth exterior surface. For spray of dip coating, such material tends to yield a grainy surface that may be expected to catch dust or dirt, decreasing the arc and track resistance of the article made of the cured position. Whatever the mode of use of the composition, satisfactory results are obtained with highly refined, white chyrsotile short-fiber Coalinga asbestos, such as that described in US. Pat. No. 3,324,073 and sold by Union Carbide Chemical Co. under the designation R.G. No. 144. Such Coalinga asbestos may be used to the extent of, for example, about 1-6 parts per 100 of resin.

The foregoing are the essential ingredients of the composition, but it may also contain others, such as catalysts, participating reaction accelerators, fireproofing agents, flame-retardants, dyes, or other coloring agents, etc.

As a catalyst for the curing reaction, if one is used, we prefer to use dibenzylmethylamine. Most of the other known catalysts for curing epoxy resins have the drawback that they worsen the performance of .the composition in arced SP gas. We may use, for example, 0.5 to 2 parts by weight of the amine per 100 parts of resin.

As a participicating reaction accelerator, we may use in some instance a mixture of sodium alcoholate suspended in polyols, such as that sold by Ciba Chemical Co. under the mark 065. This material cannot be used when magnesite is used in place of aluminum trihydrate, since it reacts with the magnesite instead of with the resin molecules. When used with compositions containing aluminum trihydrate, the material is added in quantities of about -15 parts by weight per 100 parts of resin.

The above ingredients are all mixed at 50-60 C. in a flask or beaker. A viscous liquid results. This may be used as such, or it may be thinned with an appropriate organic solvent, such as toluene, benzene, acetone, ethanol, petroleum ether, diethyl ether, or the like, depending upon the manner of intended use.

The use of the composition will be described with reference to the making of a feed tube for an extra-high-voltage power circuit breaker of the type utilizing SF gas. Such tubes are cylindrical, about 3 inches in diameter and about 12-16 feet long, with a wall thickness of about A-Vz inch. Embedded therein are reinforcing fibers such as wire or thread or cloth of glass, polyester, or the like. Those skilled in the art will understand, from the following description, how the composition would be used to make other objects for use in an environment of arced SF One way of making a feed tube is to wind the glass fiber, wetted with resin, onto a mandrel to form a tube, cure, withdraw the mandrel, grind the outside diameter to size, dip the tube into the composition, and then cure the composition, as by baking for 3.5-4.5 hours at 150 C. The dipping and baking may be repeated, if desired, to obtain a thicker coat of cured resin composition, but in most instances, this is not necessary.

Another way is to dilute the composition with solvent, warm it slightly (not necessary, but helpful), spray it onto the mold-release-coated mandrel, gel, wind the resin-wet glass filaments, cure, withdraw the mandrel, grind the outside diameter to size, spray the exterior of the tube with the composition, and cure.

Still another way is to proceed as described immediately above until there is obtained the coated and filamentwound mandrel, ready for the second spraying. Instead, the mandrel is removed and the tube is placed into a mold, preferably after grinding the outside diameter to size, and

the composition is cast into place on at least the exterior of the tube. The piece is then baked to effect the cure.

The invention described is illustrated by the specific examples hereinbelow, in connection with which there are given data resulting from certain tests, which will first be described, in order that a complete understanding may be had of the significance of the data there presented.

In one test, hereinafter referred to as the thermal cycling test, a one-inch wide ring section of an epoxy glass filament wound tube A- /z inch thick is used. This tube section is coated with the test composition being evaluated. The sample is placed for 1 hour in a cold box where the temperature is 35 C., permitted to stand for 15-30 minutes at room temperature, and then placed for /2 hour in an oven at a temperature of 120 C., and then permitted to stand for 15 minutes at room temperature. A complete test comprises ten such cycles. The sample is examined for cracks in the coating in each cycle, just before it is placed into the oven. To be satisfactory, a sample must exhibit no cracks. 7

Another test, hereinafter called the arced SP test, measures the resistance of the material to chemical attack by reactive entities present in an environment of arced SF As the materials involved must be extremely resistant to such reactive entities, so as to be capable of withstanding exposure to such an environment for such long periods of time as 30 years, it is apparent that the test for the existence of chemical attack must be a highly sensitive one. Accordingly, there was used a test, working with, for example, a sample 2 inches square by %%a inch thick, provided'with electrodes 0.25 or 0.1 inch apart (this may conveniently be done by painting electrodes onto the sample piece, using silver paint) and mounted within an autoclave having an internal capacity of 300 cubic inches and provided with suitably spaced electrodes and with shielding means between'those electrodes and the sample. The autoclave, with the sample mounted within it, is sparged with SP gas, sealed, and then pressurized with dry (under 50 ppm. moisture) SF gas. The contents of the autoclave are heated to 55 C., and then an arc is drawn between the electrodes to generate reactive entities within the pressurized (38 p.s.i.g.) SF gas. The intensity of the electrical-arc treatment of the SF gas is kilowatt-seconds. Resistance measurements are taken across the above-mentioned gap of 0.25 to 0.1 inch at various times: First, one minute after conclusion of the arcing, and then 24 hours later, when the test cell has been permitted to cool at room temperature, and a third time, after the test cell has again been heated to 55 C. The resistance values obtained are in megohms, and the lowest of the three readings is reported as the result of the test. Usually, this is the value from the first of the three readings. Although values of 500 megohms or higher may be considered satisfactory, it is preferred that the invention be practicedwith materials that give values of 10,000 megohms or higher in this test.

Another test employed is the differential wet arc and track test, which is conducted in air, rather than in SP gas. This test is ASTM Standard Test D-2302-64T.

Yet another test used is that designated the moist highpressure SF arcing test, which measures are and track resistance in moist high-pressure SP Samples substantially similar are used, and electrodes are painted on them, one inch apart. The sample is then put into a cell, which is provided with pressurized SP gas and a small controlled quantity of moisture. If necessary, the cell is cooled, to begin condensation of moisture onto the sample as dew. Electric current is then applied to the electrodes, starting at an applied potential of 1 kilovolt. This causes a light, scintillation-type arcing to begin to play back and forth across the surface of the sample between the two electrodes. The arcing is continued, with the applied voltage being progressively increased, for example, at the rate of 1 kilovolt per minute, until arcing of a different kind, i.e., more continuous, is observed. The light scintillation-type arcing causes the generation of reactive entities in the SP gas and, at the same time, tends to cause, as does any arcing along a moist surface of a synthetic-resin part, degradation of a portion of the resin to Examples of the practice of the invention, together with results obtained with a standard phenolic tube used as a control, are presented in the following Table I:

. TABLE I carbon. If the material is susceptible to tracking, this 1 degradation takes the form, at a relatively low applied Exampe voltage, of the development of a track of carbon between Control I II III IV V the electrodes, constituting a path of low resistance and Ingredients parts/wt. leading to the development of more continuous arcing, of Resin Y 170 (i) 100 100 100 the kind mentioned above. When the continuous arcing 0 develops, the current passing between the two electrodes dude 60 70 75 60 65 on the sample increases above a threshold value such as gfig ggggg fi f (1) 15 10 or 30 milliamperes, so that it is convenient to conduct Aluminum trihydrate" (i) 175 207 175 175 7; the test by having in the line supplying the impressed voltiggg gg fighg ffi f: E $3 g: g 5 age to the electrodes on the sample a current-sensitive 15 Test results: I I relay that stops the test whenever that threshold value of gggq gg ggggg 115%] E E current is reached. By reading, then, the values of the im- Thermal cycling. P P P P I P pressed current at the time that the relay operates, there ammg 3 13 12 is obtained an indication of the arc and track resistance of 1 Standard phenolic tube. the p d 20 Norn.-F=tailed; P=passed; E=exce1lent; I=infiuite.

As an alternative to the SE; arcing test, there is the fee TIT From the foregoing comparing Examples I and II with 2:22 El i 3,5 in 2 3 325 g ii g g g f giga Examples III-V, it is seen that the results with the more coated on its inside cylindrical surface with the test com- 2:; 521 622 11 gf zggfliigf zggg :3 posmon and the e-nds of-the feed tuba Sectlon are the-n 25 especially in the arced SP test. Examples III-V show that Closed by means of Inch-Huck i g of f g resn in some instances relatively small changes in the amounts tt'n ec ro es ma e g? iiggii,ffi gfiihi fi ari are p laiid against the t t used of polyazelaic polyanhydride and hexahydrophthalic surface, one inch apart. The tube is then positioned at an ahhydrlfie can glean l it t t a f t g angle 45 with respect to the horizontal and is charged l t e the d g l ies t y e3 or can e0 e Te with SF as to 240 .s.i. To the u r end of the tube, Su 5 111 e time s there is at a t f cubic ggg per minute, It should be recognized that there are differences in the water that contains 0.1% of a non-ionic wetting agent and cohthibutieh to flexibility arising out of the Cholee of Y has a resistivity of 4 kiloohms per centimeter, this water gt igf t tep f i ii g t d ltlfi lgg wgfi li i e gg lg zg flowin over the electrodes. After the Water has flowed r 1 Ta 103 O over the electrodes for 5 minutes, a 5 kilovolt potential is 30 optimize the flexibility of the Composition, as to Satls' applied across the electrodes. Scintillations slowly start faeteflly P h thermal Cycle test, y Stlll P all the and play across the test surface. The test continues for 10 other tests ll h 1 fl b1 1 l minutes, unless the test surface fails before that time, for For f P e an In erent Y more eXl e eye 03 p example, by developing a carbon track or an overall 40 epoxy resm hke CY 181 (E?(amP1e Table II) W111 electrical resistance low enough that the current between gixi g g g gg gggiz gg i f i ff gigg hl gtgr & the electrodes rises to 20 milliamperes. In either event, p p I Table D the inherenflg, greater flex the i t W111 use sufficlently to zictwate a mlay set 9 ibility of the cycloaliphatic epoxy resin compensates some- 20 milliamperes. The results of this test are reported in What for requirement for use of PAPA to achieve number, of seconfis dur at10n of test with an Indication (T) creased flexibility. Particularly good results in all required of the instances 1n WhlCh a carbon track was observed on Properties attend our preferred compositions wherein the the failed test sample. A standard phenolic feed tube, 1.e., ratio of PAPA to HHPA is in the range of about 4:1 to one made in accordance with the prior art, fails in this 5; test in less than 12 Seconds, and Oh the average in less Additional results are presented in the following Table than 4 seconds, tracking being observed. II:

TABLE II Controls Example I II VI VII VIII IX X XI XII XIII XIV Ingredients, parts/wt;

(gEpi-R 51 Polyazelaic poly hyclr Hexahydrophthalic anhydride- Aluminum trihydrate Benzyldimethyl amine Asbestos R G-144" Test results:

Arced SFt, megohms ASTM D-2302-64T Thermal cycling- FTT'I, seconds..

1 Standard phenolic tube.

aWHi-t G 8mm 555 NoTE.-F=failed; P passed; E =exeellent; I=infinite, T =tracked.

The foregoing results show that with the preferred cycloaliphatic resin and proper amounts of other ingredients, excellent results are obtained (Examples XII-XIV), the last of these constituting the best mode now known for practicing the invention.

While we have shown and described herein certain embodiments of our invention, we intend to cover as well as any change or modification therein which may be made without departing from its spirit and scope.

We claim as our invention:

1. Thixotropic compositions of matter for use in SF environments consisting essentially of:

(a) 100 parts by weight of a monomeric cycloaliphatic epoxy containing at least one cycloaliphatic ring,

(b) about 30-115 parts by weight of a fiexibilizing agent selected from the group consisting of a polyazelaic polyanhydride (average molecular weight 2100-2500) and hexahydrophthalic anhydride.

() about 120-250 parts by weight of filler material selected from the group consisting of aluminum trihydrate and naturally occurring magnesite, and

(d) about 1-6 parts by weight of a thixotroping agent selected from the group consisting of finely divided asbestos and short-fiber white chrysotile asbestos.

2. Compositions as defined in claim 1 wherein the cycloaliphatic epoxy has the structure a viscosity of 350-450 cp. at 25 C. and an epoxide equivalent weight of 126-140.

3. The composition of claim 1 wherein the fiexibilizing agent is a mixture of the polyazelaic polyanhydride and hexahydrophthalic anhydride.

4. Compositions as defined in claim 1, characterized in that said cycloaliphatic epoxy is one having a backbone structure containing a pair of cycloaliphatic rings joined by a bridge, with epoxy oxygen atoms joined to vicinal carbon atoms comprising said rings.

5. Compositions as defined in claim 4, characterized in that said filler material is aluminum trihydrate and said thixotroping agent is short-fiber white chrysotile asbestos.

6. Compositions as defined in claim 4, characterized in that said epoxy has a backbone structure that contains a bridge containing not more than about 5 atoms in the direct chain between said rings.

7. Compositions as defined in claim 6, characterized in that said filler material is aluminum trihydrate and said thixotroping agent is short-fiber white chrysotile asbestos.

8. An insulated article in an environment of SF gas subject to arcing said article having a flexible insulating surface adapted to be exposed to said gas, said surface having chemical resistance in arced SP and resistance to track degradation in an environment of SP said insulating surface consisting essentially of the cured reaction product of:

(a) 100 parts by weight of a monomeric cycloaliphatic epoxy containing at least one cycloaliphatic ring,

(b) about 30-115 parts by weight of a flexibilizing agent selected from the group consisting of polyazelaic polyanhydride (average molecular weight 2100-2500) and hexahydrophthalic anhydride,

(c) about 120-250 parts by weight of filler material selected from the group consisting of aluminum trihydrate and naturally occurring magnesite, and

(d) about 1-6 parts by weight of a thixotroping agent selected from the group consisting of finely divided asbestos and short-fiber white chrysotile asbestos.

9. The article of claim 8 wherein the cycloaliphatic epoxy has the structure RCO-OCH R Where R is a cycloaliphatic ring having an oxygen atom connected to a pair of vicinal carbon atoms thereof with a viscosity 12 of 350-450 cp. at 25 C. and an epoxide equivalent weight of 126-140.

10. The article of claim 8 wherein the fiexibilizing agent is a mixture of the polyazelaic polyanhydride and hexahydrophthalic anhydride.

11. An article as defined in claim 8, characterized in that said article comprises a part of an extra-high voltage circuit breaker.

12. An article as defined in claim 11, characterized in that said article is a feed tube.

13. An article as defined in claim 8, characterized in that, in said reaction product, said thixotroping agent is short-fiber white chrysotile asbestos and said filler material is aluminum trihydrate.

14. An article as defined in claim 8, characterized in that said cycloaliphatic epoxy is one having a backbone structure containing a pair of cycloaliphatic rings joined by a bridge, with epoxy oxygen atoms joined to'vicinal carbon atoms comprising said rings.

15. An article as defined in claim 14, characterized in that said epoxy has a backbone structure that contains a bridge containing not more than about 5 atoms in the direct chain between said rings.

16. An article as defined in claim 15, further characterized in that, in said reaction product, said filler material is aluminum trihydrate and said thixotroping agent is short-fiber white chrysotile asbestos.

17. An article as defined in claim 16, characterized in that said article comprises a part of an extra-high voltage circuit breaker.

18. An article as defined in claim 17, characterized in that said article is a feed tube.

19. Thixotropic compositions of matter for use in SP environments consisting essentially of:

(a) parts by weight of a diglycidyl ether epoxy consisting essentially of a resin having the structural where n=an integer from about 4 to 30; and R and R are lower alkyl radicals selected from the group consisting of C to C (b) about 30-115 parts by weight of a fiexibilizing agent selected from the group consisting of polyazelaic polyanhydride (average molecular weight 2100-2500), hexahydrophthalic anhydride and mixtures thereof,

(0) about -250 parts by weight of filler material selected from the group consisting of aluminum trihydrate and naturally occurring magnesite, and

(d) about 1-6 parts by weight of short-fiber white chrysotile asbestos.

20. An insulated article in an environment of SP gas subject to arcing said article having a flexible insulating surface adapted to be exposed to said gas, said surface having chemical resistance in arced SP and resistance to track degradation in an environment of SP said insulating surface consisting essentially of the cured reaction product of:

(a) 100 parts by weight of a diglycidyl ether epoxy consisting essentially of a resin having the structural 13 where n=an integer from about 4 to 30; and R and R are lower alkyl radicals selected from the group consisting of C1 to C (b) about 30-115 parts by weight of a flexibilizing agent selected from the group consisting of polyazelaic polyanhydride (average molecular weight 2100-2500) and hexahydrophthalic anhydride,

(c) about 120250 parts by weight of filler material selected from the group consisting of aluminum trihydrate and naturally occurring magnesite, and

(d) about 1-6 parts by weight of short-fiber white chrysotile asbestos.

21. An article as defined in claim 20, characterized in that said article comprises part of an extra-high voltage circuit breaker.

22. An article as defined in claim 21, characterized in that said article is a feed tube.

References Cited UNITED STATES PATENTS 3,645,899 2/1972 Linson 26037 EP X OTHER REFERENCES R. G. Black et al., PAPA Offers Many Advantages as a Converter for Epoxies, Plastus Technology (March 1964), pp. 27 10.

American Chemical Society, Chemical & Engineering News, vol. 44, No. 41 (October 1966), pp. 57 and 58.

Dow Chemical Company, Bulletin #190-105-69, p. 1 (1969).

ALLAN LIEBERMAN, Primary Examiner I. M. PERSON, Assistant Examiner 

